Dorsiflexor Muscle Oxygenation During Low, Moderate and Submaximal Sustained Isometric Contraction.

Sustained isometric contractions of skeletal muscles produce intramuscular pressures that lead to blood flow restriction. Thus, we have the paradox of rising O2 demand due to muscle activity and at the same time reduced blood flow. The aim was to assess muscle oxygenation during sustained isometric low (30%), moderate (60%) and submaximal [90% of maximal voluntary contraction (MVC)] contraction of the dorsiflexor muscle. Experiments were conducted on the dominant (right) leg of 8 male students (age 19 ± 2 years, weight 75 ± 6 kg). Tissue oxygen saturation (StO2) was recorded from the tibialis anterior using near-infrared spectroscopy. StO2 was higher at 30% compared to both 60% and 90% MVC at all time points after the start of the exercise and higher at 60% than 90%. This indicates that the supply of O2 did not keep up with its consumption. During arterial occlusion the minimal StO2 reached 52%, which is significantly higher than StO2 during 60% and 90% MVC. After each contraction there was a large and immediate hyperemic response, whose resaturation rate continuously increased from 30% to 60% to 90% MVC. The StO2 resaturation rate was positively correlated with the MVC, indicating a vasodilation depending on the intensity of the exercise.

Morphological defects in cotton hairs and the nature of their origin.

In vivo observations of the origin of native defects in cotton hairs were carried out during their development in unopened cotton bolls. It is shown that the formation of these structural defects is related to features of their packing inside the cotton bolts during the formation of the boll segments. A mechanism explaining the origination of these morphological defects is proposed. It is based on the hydrodynamic properties of the cytoplasm at the sites of bending in developing cotton hairs.